/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 * 
 *      http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package jacky.lanlan.song.util.builder;

/**
 * <p>
 * Assists in implementing {@link Object#hashCode()} methods.
 * </p>
 * 
 * <p>
 * This class enables a good <code>hashCode</code> method to be built for any
 * class. It follows the rules laid out in the book <a
 * href="http://java.sun.com/docs/books/effective/index.html">Effective Java</a>
 * by Joshua Bloch. Writing a good <code>hashCode</code> method is actually
 * quite difficult. This class aims to simplify the process.
 * </p>
 * 
 * <p>
 * All relevant fields from the object should be included in the
 * <code>hashCode</code> method. Derived fields may be excluded. In general,
 * any field used in the <code>equals</code> method must be used in the
 * <code>hashCode</code> method.
 * </p>
 * 
 * <p>
 * To use this class write code as follows:
 * </p>
 * 
 * <pre>
 *  public class Person {
 *    String name;
 *    int age;
 *    boolean smoker;
 *    ...
 * 
 *    public int hashCode() {
 *      // you pick a hard-coded, randomly chosen, non-zero, odd number
 *      // ideally different for each class
 *      return new HashCodeBuilder(17, 37).
 *        append(name).
 *        append(age).
 *        append(smoker).
 *        toHashCode();
 *    }
 *  }
 * </pre>
 * 
 * <p>
 * If required, the superclass <code>hashCode()</code> can be added using
 * {@link #appendSuper}.
 * </p>
 * 
 * @author Stephen Colebourne
 * @author Gary Gregory
 * @author Pete Gieser
 * @since 1.0
 * @version $Id: HashCodeBuilder.java 447989 2006-09-19 21:58:11Z ggregory $
 */
public class HashCodeBuilder {

	/**
   * Constant to use in building the hashCode.
   */
	private final int iConstant;

	/**
   * Running total of the hashCode.
   */
	private int iTotal = 0;

	/**
   * <p>
   * Uses two hard coded choices for the constants needed to build a
   * <code>hashCode</code>.
   * </p>
   */
	public HashCodeBuilder() {
		iConstant = 37;
		iTotal = 17;
	}

	/**
   * <p>
   * Two randomly chosen, non-zero, odd numbers must be passed in. Ideally these
   * should be different for each class, however this is not vital.
   * </p>
   * 
   * <p>
   * Prime numbers are preferred, especially for the multiplier.
   * </p>
   * 
   * @param initialNonZeroOddNumber
   *          a non-zero, odd number used as the initial value
   * @param multiplierNonZeroOddNumber
   *          a non-zero, odd number used as the multiplier
   * @throws IllegalArgumentException
   *           if the number is zero or even
   */
	public HashCodeBuilder(int initialNonZeroOddNumber,
			int multiplierNonZeroOddNumber) {
		if (initialNonZeroOddNumber == 0) { throw new IllegalArgumentException(
				"HashCodeBuilder requires a non zero initial value"); }
		if (initialNonZeroOddNumber % 2 == 0) { throw new IllegalArgumentException(
				"HashCodeBuilder requires an odd initial value"); }
		if (multiplierNonZeroOddNumber == 0) { throw new IllegalArgumentException(
				"HashCodeBuilder requires a non zero multiplier"); }
		if (multiplierNonZeroOddNumber % 2 == 0) { throw new IllegalArgumentException(
				"HashCodeBuilder requires an odd multiplier"); }
		iConstant = multiplierNonZeroOddNumber;
		iTotal = initialNonZeroOddNumber;
	}

	/**
   * <p>
   * Append a <code>hashCode</code> for a <code>boolean</code>.
   * </p>
   * <p>
   * This adds <code>iConstant * 1</code> to the <code>hashCode</code> and
   * not a <code>1231</code> or <code>1237</code> as done in
   * java.lang.Boolean. This is in accordance with the <quote>Effective Java</quote>
   * design.
   * </p>
   * 
   * @param value
   *          the boolean to add to the <code>hashCode</code>
   * @return this
   */
	public HashCodeBuilder append(boolean value) {
		iTotal = iTotal * iConstant + (value ? 0 : 1);
		return this;
	}

	/**
   * <p>
   * Append a <code>hashCode</code> for a <code>boolean</code> array.
   * </p>
   * 
   * @param array
   *          the array to add to the <code>hashCode</code>
   * @return this
   */
	public HashCodeBuilder append(boolean[] array) {
		if (array == null) {
			iTotal = iTotal * iConstant;
		} else {
			for (int i = 0; i < array.length; i++) {
				append(array[i]);
			}
		}
		return this;
	}

	// -------------------------------------------------------------------------

	/**
   * <p>
   * Append a <code>hashCode</code> for a <code>byte</code>.
   * </p>
   * 
   * @param value
   *          the byte to add to the <code>hashCode</code>
   * @return this
   */
	public HashCodeBuilder append(byte value) {
		iTotal = iTotal * iConstant + value;
		return this;
	}

	// -------------------------------------------------------------------------

	/**
   * <p>
   * Append a <code>hashCode</code> for a <code>byte</code> array.
   * </p>
   * 
   * @param array
   *          the array to add to the <code>hashCode</code>
   * @return this
   */
	public HashCodeBuilder append(byte[] array) {
		if (array == null) {
			iTotal = iTotal * iConstant;
		} else {
			for (int i = 0; i < array.length; i++) {
				append(array[i]);
			}
		}
		return this;
	}

	/**
   * <p>
   * Append a <code>hashCode</code> for a <code>char</code>.
   * </p>
   * 
   * @param value
   *          the char to add to the <code>hashCode</code>
   * @return this
   */
	public HashCodeBuilder append(char value) {
		iTotal = iTotal * iConstant + value;
		return this;
	}

	/**
   * <p>
   * Append a <code>hashCode</code> for a <code>char</code> array.
   * </p>
   * 
   * @param array
   *          the array to add to the <code>hashCode</code>
   * @return this
   */
	public HashCodeBuilder append(char[] array) {
		if (array == null) {
			iTotal = iTotal * iConstant;
		} else {
			for (int i = 0; i < array.length; i++) {
				append(array[i]);
			}
		}
		return this;
	}

	/**
   * <p>
   * Append a <code>hashCode</code> for a <code>double</code>.
   * </p>
   * 
   * @param value
   *          the double to add to the <code>hashCode</code>
   * @return this
   */
	public HashCodeBuilder append(double value) {
		return append(Double.doubleToLongBits(value));
	}

	/**
   * <p>
   * Append a <code>hashCode</code> for a <code>double</code> array.
   * </p>
   * 
   * @param array
   *          the array to add to the <code>hashCode</code>
   * @return this
   */
	public HashCodeBuilder append(double[] array) {
		if (array == null) {
			iTotal = iTotal * iConstant;
		} else {
			for (int i = 0; i < array.length; i++) {
				append(array[i]);
			}
		}
		return this;
	}

	/**
   * <p>
   * Append a <code>hashCode</code> for a <code>float</code>.
   * </p>
   * 
   * @param value
   *          the float to add to the <code>hashCode</code>
   * @return this
   */
	public HashCodeBuilder append(float value) {
		iTotal = iTotal * iConstant + Float.floatToIntBits(value);
		return this;
	}

	/**
   * <p>
   * Append a <code>hashCode</code> for a <code>float</code> array.
   * </p>
   * 
   * @param array
   *          the array to add to the <code>hashCode</code>
   * @return this
   */
	public HashCodeBuilder append(float[] array) {
		if (array == null) {
			iTotal = iTotal * iConstant;
		} else {
			for (int i = 0; i < array.length; i++) {
				append(array[i]);
			}
		}
		return this;
	}

	/**
   * <p>
   * Append a <code>hashCode</code> for an <code>int</code>.
   * </p>
   * 
   * @param value
   *          the int to add to the <code>hashCode</code>
   * @return this
   */
	public HashCodeBuilder append(int value) {
		iTotal = iTotal * iConstant + value;
		return this;
	}

	/**
   * <p>
   * Append a <code>hashCode</code> for an <code>int</code> array.
   * </p>
   * 
   * @param array
   *          the array to add to the <code>hashCode</code>
   * @return this
   */
	public HashCodeBuilder append(int[] array) {
		if (array == null) {
			iTotal = iTotal * iConstant;
		} else {
			for (int i = 0; i < array.length; i++) {
				append(array[i]);
			}
		}
		return this;
	}

	/**
   * <p>
   * Append a <code>hashCode</code> for a <code>long</code>.
   * </p>
   * 
   * @param value
   *          the long to add to the <code>hashCode</code>
   * @return this
   */
	public HashCodeBuilder append(long value) {
		iTotal = iTotal * iConstant + ((int) (value ^ (value >> 32)));
		return this;
	}

	/**
   * <p>
   * Append a <code>hashCode</code> for a <code>long</code> array.
   * </p>
   * 
   * @param array
   *          the array to add to the <code>hashCode</code>
   * @return this
   */
	public HashCodeBuilder append(long[] array) {
		if (array == null) {
			iTotal = iTotal * iConstant;
		} else {
			for (int i = 0; i < array.length; i++) {
				append(array[i]);
			}
		}
		return this;
	}

	/**
   * <p>
   * Append a <code>hashCode</code> for an <code>Object</code>.
   * </p>
   * 
   * @param object
   *          the Object to add to the <code>hashCode</code>
   * @return this
   */
	public HashCodeBuilder append(Object object) {
		if (object == null) {
			iTotal = iTotal * iConstant;

		} else {
			if (object.getClass().isArray() == false) {
				// the simple case, not an array, just the element
				iTotal = iTotal * iConstant + object.hashCode();

			} else {
				// 'Switch' on type of array, to dispatch to the correct handler
				// This handles multi dimensional arrays
				if (object instanceof long[]) {
					append((long[]) object);
				} else if (object instanceof int[]) {
					append((int[]) object);
				} else if (object instanceof short[]) {
					append((short[]) object);
				} else if (object instanceof char[]) {
					append((char[]) object);
				} else if (object instanceof byte[]) {
					append((byte[]) object);
				} else if (object instanceof double[]) {
					append((double[]) object);
				} else if (object instanceof float[]) {
					append((float[]) object);
				} else if (object instanceof boolean[]) {
					append((boolean[]) object);
				} else {
					// Not an array of primitives
					append((Object[]) object);
				}
			}
		}
		return this;
	}

	/**
   * <p>
   * Append a <code>hashCode</code> for an <code>Object</code> array.
   * </p>
   * 
   * @param array
   *          the array to add to the <code>hashCode</code>
   * @return this
   */
	public HashCodeBuilder append(Object[] array) {
		if (array == null) {
			iTotal = iTotal * iConstant;
		} else {
			for (int i = 0; i < array.length; i++) {
				append(array[i]);
			}
		}
		return this;
	}

	/**
   * <p>
   * Append a <code>hashCode</code> for a <code>short</code>.
   * </p>
   * 
   * @param value
   *          the short to add to the <code>hashCode</code>
   * @return this
   */
	public HashCodeBuilder append(short value) {
		iTotal = iTotal * iConstant + value;
		return this;
	}

	/**
   * <p>
   * Append a <code>hashCode</code> for a <code>short</code> array.
   * </p>
   * 
   * @param array
   *          the array to add to the <code>hashCode</code>
   * @return this
   */
	public HashCodeBuilder append(short[] array) {
		if (array == null) {
			iTotal = iTotal * iConstant;
		} else {
			for (int i = 0; i < array.length; i++) {
				append(array[i]);
			}
		}
		return this;
	}

	/**
   * <p>
   * Adds the result of super.hashCode() to this builder.
   * </p>
   * 
   * @param superHashCode
   *          the result of calling <code>super.hashCode()</code>
   * @return this HashCodeBuilder, used to chain calls.
   * @since 2.0
   */
	public HashCodeBuilder appendSuper(int superHashCode) {
		iTotal = iTotal * iConstant + superHashCode;
		return this;
	}

	/**
   * <p>
   * Return the computed <code>hashCode</code>.
   * </p>
   * 
   * @return <code>hashCode</code> based on the fields appended
   */
	public int toHashCode() {
		return iTotal;
	}

}
